The Valve Index is in a pretty high demand ahead of Half-Life Alyx's launch (on March 23). That is expected, really, but due to the coronavirus crisis, the manufacturers in China are unable to produce enough Valve headsets, so backorder is currently the only option available.
Valve did confirm that people will eventually be able to buy the Index VR set again, but they didn't give an exact date. That information came out a few weeks ago, but today we know that the restock is planned for March 9, 10 AM Pacific time.
Timing is crucial here and Valve already stated that restock won't be able to meet the current demand. We'll see how it will all play out when the sales begin, however.
Get yourself ready for Monday and make sure you have your cash ready!